1. Field of the Invention
The present invention relates to an optical pickup capable of recording information on or reproducing information from an optical recording medium, and more particularly, to an optical pickup adopting a light-emitting diode (LED) capable of forming a light spot of an appropriate size for a high-density recording/reproduction.
2. Description of the Related Art
In general, in an optical recording/reproduction field of technology, an optical disk such as a laser disk (LD), a compact disk (CD) or a digital versatile disk (DVD) has been focused on as an optical recording medium capable of recording a large amount of information. In particular, the DVD has been highlighted due to its large scale information processing capability. In order to increase the recording density of the DVD, it is necessary to minimize the size of the light spot formed on the recording surface of the DVD.
Referring to FIG. 1, a conventional optical pickup includes a light source 11 for generating/emitting a laser beam, a beam splitter 13 for converting the traveling path of the incident light, an objective lens 14 for condensing the light emitted from the light source 11 via the beam splitter 13, and a photodetector 16 for receiving the light incident via the beam splitter 13 after being reflected from an optical disk 1. The light source 11 is a semiconductor laser for generating and emitting the laser beam. The photodetector 16 receives the light reflected from the optical disk 1 and performs a photoelectric conversion to detect a radio frequency (RF) signal, a tracking error signal and a focus error signal.
A collimating lens 12 is provided between the light source 11 and the beam splitter 13, which collimates the divergent light emitted from the light source 11. Also, a light reception lens 15 is arranged between the beam splitter 13 and the photodetector 16, which causes astigmatism so that a focus error signal can be detected.
As described above, when forming a light spot on the optical disk 1 using an optical pickup having the above structure, the size of the light spot is determined by the following equation (1). EQU size of light spot.congruent.
##EQU1##
where .lambda. represents the wavelength of the light source 11 of the optical pickup, and NA represents the numerical aperture of the objective lens 14 of the optical pickup.
Thus, if the objective lens 14 of the optical pickup has a predetermined numerical aperture, a shorter wavelength of the light emitted from the light source 11 will form a smaller light spot. On the other hand, since the light source 11 is a semiconductor laser, it is difficult for the wavelength of the light to be approximately 635 nm. Thus, if the numerical aperture of the objective lens is 0.6, the size of the light spot formed on the optical disk is approximately 1.08 .mu.m based on the equation (1). Thus, it is difficult to record optical information of 5 gigabytes or more on an optical disk having a diameter of 130 mm.